Orange edges in object mode
In Blender the selected/active object are outlined in edit mode by varous  coloured lines which by default are highlite only on the meshes's boundaries, aka the edges who are shared by less than two faces



Notice that this behaviour make clearly visible those objects who behave like paths or profiles, who have edges not connecting any faces and fall in the category explained above.



In your case you probably have both cases in the same mesh, overlayed.



If you want to get rid of the edges not connecting any faces, you can take advantage of the Delete Loose tool: